As one method for improving in-plane uniformity of CMP (Chemical Mechanical Polishing), Japanese Patent Application Laid-Open No. 2003-175455 discloses a method for detecting an eddy current generated on a surface of a wiring material at the time of CMP, monitoring distribution of a residual film thickness of the wiring material and feedback-controlling a head pressure so that CMP is carried out flatly.
In order to heighten polishing throughput, the wiring material should be polished in two steps. In this case, after the wiring material is polished at a first polishing step so that its residual film thickness becomes about 200 nm and the surface is flattened, the remaining wiring material is polished at a second polishing step.
However, when the wiring material is polished at the second polishing step, the residual film thickness of the wiring material is extremely small or becomes zero as the polishing progresses. For this reason, distribution of the film thickness cannot be monitored by an eddy current. That is, the distribution of the film thickness of the wiring material can be controlled practically only at the first polishing step.
In the case where different polishing pads are used at the first polishing step and the second polishing step like the case of using a multi-platen polishing device, polishing rate profiles are different between these polishing steps. For this reason, even if the residual film thickness of the wiring material is controlled flatly at the first polishing step, the polishing distribution is deflected at the second polishing step, and occasionally the film thickness of a formed wiring layer varies in a wafer plane.
The similar problem arises not only in the case of CMP of the wiring material but also in the case of CMP of an insulating material to be used in a step of forming an element separation film by means of an STI method, for example.